Why are soda cans cylindrical and have a curved bottom?

We are so used to having a soft drink or a beer in a can of 6 cm in diameter, 12 cm high and with a content of 330 ml of liquid that we ignore its design. When an engineer sits down, takes paper and pencil and thinks about the design of a container that can contain a gaseous liquid, the first idea that passes through the neurons is to find a way in which the internal pressure is distributed homogeneously. The problem with this approach is that if we think about its fixing on a flat surface it would be uncomfortable and impractical, in addition to the fact that both storage and transport would be rather cumbersome. With the spherical shape, 26% of the stacked volume would be wasted. The alternative passes through an orthohedral geometric figure, that is, an orthogonal rectangular prism. In this case the weak point is in the edges, as they may break if hit or pressed.

The alternative is the cylinder. When making pressed cans in a mould with this shape, the corners are no longer a problem, making them superfluous to reinforce to withstand transport. Furthermore, this form satisfactorily solves the problem of stacking, with a cylinder we can operate up to 91% of the volume. A cylindrical can, however, has radial symmetry: the addition of a dome to the base and the rounding of the edges can simulate the state of the membrane, through which the internal pressure increases rigidity and prevents deformity. The process of printing a cylinder is simpler -it is done at once- than when it has an orthohedral shape, since it requires four steps, being, therefore, more expensive. If we now think about the packaging process, it is much easier to follow a cylindrical guide than a square one, because at high speeds they could hit the rails, while the cylindrical morphology flows much better. It is estimated that 310 cm 2 of raw material are needed to make a 33 cl can in the case of cylindrical shape, a figure that rises to 340 cm 2 if you choose an orthohedral shape, so the first is much more ecological. Currently 70% of the material with which the cans are made comes from recycling, if to this we add that every second in the world are produced about 15,000 cans -almost half a trillion per year- It is easy to understand that the production process is still much more efficient than we might assume a priori. Finally, with the diameter of the lids of beverage cans, in the last six decades it has been reduced by six millimetres - from 60 mm to 54 mm - which has saved about ninety million pounds of aluminum per year. So now you know that the next time you open a can, whatever it contains, it’s time to toast to the health of engineering, the branch of science that made this amazing design possible.